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Vehicle incab booming perception, a low frequency response of the structure to the various excitations presents a challenging task for the NVH engineers. The excitation to the structure causing boom can either be power train induced, depending upon the number of cylinders or the road inputs, while transfer paths for the excitation is mainly through the power train mounts or the suspension attachments to the body. The body responds to those input excitations by virtue of the dynamic behavior mainly governed by its modal characteristics. This paper explains in detail an integrated approach, of both experimental and numerical techniques devised to investigate the mechanism for boom noise generation. It is therefore important, to understand the modal behavior of the structure. The modal characteristics from the structural modal test enable to locate the natural frequencies and mode shapes of the body, which are likely to get excited due to the operating excitations.

Noise & Vibration refinement of automotive vehicles is becoming important parameter due to its influence on environmental aspect and comfort perceived by occupants. NVH parameters are driving factors in current vehicle design strategy. Drivers comfort is extremely important, and driver’s expectations from commercial and heavy-duty trucks are as good as refined passenger cars. Other trends in commercial vehicle segment such as engine downsizing, weight, cost reduction and meeting stringent emission norms have influenced vehicle design dynamics. These parameters are critical and often contribute to vehicle NVH issues. Considering these new trends in commercial vehicle segment, it becomes challenging for an NVH engineer to provide optimized solutions. NVH issues could be related to the various subsystems such as driveline, axle, transmission steering wheel etc. in the vehicle and its resonant frequencies.

In worldwide automotive markets, the migration of customers towards smaller cars having compact, fuel-efficient design is well established and accepted as an engineering challenge by global automotive OEMs. Tata Motors of India has established a precedent by developing an ultra low cost and light weight car (the Nano), and has thereby created a new market segment for such cars that are more affordable to most of the population. This is now becoming established as a brand of low cost, safe transport in both rural and urban market segments. Despite the market moving towards such compact, fuel-efficient designs, customers are unwilling to lose many of the vehicle attributes to which they have been accustomed in previous types of entry-level cars. Addressing this marketing requirement places some significant challenges before the designers of this type of car.

For an automotive exhaust system, noise level and back pressure are the most important parameters for passenger comfort and engine performance respectively. The sound quality perception of the existing silencer design was unacceptable, although the back pressure measured was below the target limit. To improve the existing design, few concepts were prepared by changing the internal elements of silencer only. The design constraints were the silencer shell dimensions, volume of silencer, inlet pipe and outlet tailpipe positions, which had to be kept same as that of the existing base design. The sound quality signal replaying and synthesizing was performed to define the desired sound quality. The numerical simulation involves 3D computational fluid dynamics (CFD) with appropriate boundary condition having less numerical diffusions to predict the back pressure. The various silencer concepts developed with this preliminary analysis, was then experimentally verified with the numerical data.

Baffle plates with heat reactive expandable foam sealants have increasingly found their applications in automotives. They are used to separate body cavities and to impede noise, water and dust propagation inside of body cavities, thus control noise intrusion into the passenger compartment. Use of these sealant materials has grown significantly as the demands to improve vehicle acoustic performance has increased. Traditionally quantification of the acoustic performance of expandable baffle samples involved making separate vehicles with and without expandable baffles and measure the incab noise to know the effect. The absolute acoustic evaluation of the baffles is very difficult as number of other vehicle parameters is also responsible for vehicle incab noise. Also, it is a time consuming and a costly method to evaluate.

The idle NVH refinement gives the customer a feel of overall quality of the vehicle. The psycho-acoustic perception of the driver/passenger during idling is primarily influenced by the power train refinement and its isolation from the passenger compartment. Power train mounting system plays a vital role in attaining the required idle NVH refinement. The modern cars being designed for higher power to weight ratio, with more powerful engines and lighter frame work has made the task of NVH refinement more difficult. The response of the lighter structure to load variation at idle due to operation of ancillary systems like HVAC, and electrical systems such as head lamps, fog lamps, wipers etc. causes discomfort to the passenger. This paper describes an approach towards identifying the key factors governing the idle vibration of the vehicle in steady state as well as in transient operation.

Quality of the sound is one of the major parameter for the occupants comfort. The vehicle noise can be broadly classified into airborne and structure borne noise contributed by numerous aggregates present in vehicle. Among different vehicle aggregates the alternator, which is an important component in vehicle electrical architecture, can be considered as a major source of airborne noise. Generally, the alternator noise is combination of mechanical, aerodynamic, and electromagnetic sources. The ratio of these sources in the overall noise varies with speed and loading pattern. The mechanical and aerodynamic noise normally depends on speed while the electromagnetic noise variation is load dependent. Alternator whining is an irritant perception of the sound quality due to electromagnetic noise. When the alternator is loaded with electrical loads (like head lamp, tail lamp, wiper and HVAC) the sound level increases further.

Success of the vehicle in the market depends on comfort provided while usage, which also includes noise, vibration and harshness (NVH). In order to achieve comfort level, the NVH levels have to be as low as possible. Powertrain is the main source of NVH, in which internal combustion engine consists of crank shaft and balancer shaft. Crank shaft gear is connected and driven by crank shaft and balanced by integral eccentric mass coupled with gear. Balancer shaft is used for additional balancing of rotating masses. Pair of crank shaft and balancer shaft gears generates noise and vibration when unbalance in the system and backlash in the gears increase while usage. The practice of interposing a vibration isolator on the surface of gear has been so far resorted for preventing transmission of vibration, therefore reduction in noise. In the work presented, balancer gear was made with sandwich design to reduce noise. Sandwich design comprises of Inner hub and outer ring with lug projections.

Comfort is a key factor in the automobile industry. Vehicles are designed to provide optimum comfort levels to passengers and drivers. The agricultural industry is a vital sector and requires long hours of operation for which comfort levels are a priority. To achieve these comfort levels Noise, Vibration, and Harshness (NVH) engineering is done, which includes computer-aided and prototype testing to troubleshoot problems and provide necessary solutions. This research work is based on the final stage of tractor development, during which an abnormal rattle noise was observed. This paper presents the airborne and structure-borne NVH study on a tractor by measuring sound pressure and vibration levels at vehicle and engine levels. A preliminary inspection of the tractor indicated the presence of abnormal noise during operation. For a detailed study, the engine was removed from the vehicle and mounted on a testbench to conduct a series of tests.

The prime target of IEA (international energy association) to reduce global average emission by 50% in 2030 has prompted focused R&D on automotive emission reduction as well as NEV (new energy vehicles). Of these strategies, engine downsizing constitutes the group of strategies employed to meet lower emission and fuel consumption targets in IC engines. Downsizing strategies have been proved successful in reducing emissions. There is widespread trend of downsizing existing engines with a goal to produce lower emissions along with equal or better performance. To achieve the stated goals downsized engines are usually charged or employ higher compression ratios. This raises NVH as well as structural issues that need further analysis. While the concept of downsizing has been studied in deep, its structural effects and NVH related issues are of concern. This paper throws light into different engine downsizing strategies and their effect on NVH.

NVH is very important topic in development of a vehicle. Legislative requirements for driver ear level, the comparison to competitor vehicles in terms of noise and vibration as well as sound quality set very challenging targets. High noise at Driver Ear Level (DEL) and tactile vibrations of tractor is the major cause of exhaustion to the operator. With growing competition there is need for the tractor manufacturers to control noise and vibration levels. Recognizing the corrective measures to reduce the noise and vibration has a greater impact in increasing the efficiency of the product and operator comfort. Objective of this paper is to control vehicle level noise and vibrations using vehicle level structure modifications. It includes airborne and structure borne NVH study on a tractor by measuring sound pressure and vibration levels at vehicle level. Single cylinder engine was mounted on light weight structure to meet the power and torque requirements in the tractor.

Legislations on vehicular noise levels are becoming stringent day by day. Also the customer expectations on the vehicle noise levels has also become more refined in the India market. Intake and exhaust flow noise levels are one of the major contributors to this overall noise level of the vehicle. These drivers have led the Indian automobile manufacturers to focus on engine and vehicle noise optimization. The 3-wheeler and 4-wheeler Quadra-cycle vehicles which are powered by single cylinder engines are more prone to high noise levels due to pulsating intake and exhaust flow dynamics caused by single firing cylinder. The study focuses on the exhaust muffler design optimization of a single cylinder engine powertrain to meet the targeted noise levels. One - Dimensional (1D) Simulation tools give significant information at the system level and reduce the time required for analysis and optimization compared to the three - dimensional (3D) CFD tools.

Reducing vehicular noise has become a crucial step in product development to meet stringent legislation and improve passenger experience. Smaller vehicles like three-wheelers and compact cars are often powered by a single cylinder engine due to product cost, packaging and weight constraints. Unlike a multi-cylinder engine where cylinders fire one after another which helps to reduce noise levels by destructive interference of pressure waves, a single cylinder engine produces higher noise levels due to firing of a single cylinder. Intake and exhaust flow noise is one of the dominant sources of vehicular noise. This study focuses on using CAE tools to reduce intake and exhaust flow noise levels to meet target noise requirements. One dimensional (1-D) gas dynamics simulation provides a good trade-off between accuracy and run-time, allowing for evaluation of multiple design iterations with acceptable accuracy in a relatively short time frame.